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Fibre-optic cables

Fibre optic cables are very different from copper ones. They carry light, not electricity, and have no need for a second cable for a 'return path'.

They can transport much greater amounts of information, and also, on a mile-for-mile basis, they are much less noisy than copper and as a result lose much less information. Although the cable is very clear, the transmitted light does fade over long distances and optical repeater stations are needed to regenerate the light, generally every 60 miles or so. At the other end of the line, the digital light signals are detected by an optical receiver and converted back into electrical signals to be sent to their destination.

Fibre optic communication uses light to pass digital information from the sender to the receiver. An electric signal is converted into pulses of light - billions of times a second - transmitted by an Light Emitting Diode or a laser beam. These pulses are focussed by a lens into the cable. Some systems send more than one signal at the same time by using lasers sending light of different wavelengths or colours.

Fibre optic cables form the backbone of today's telecommunications system and have played a huge part in making the Internet available around the world.

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